Currently, one can send a mailpiece (e.g., letter, package, etc.) through the United States Postal Service (hereafter referred to as USPS) using a postage indicium as evidence of postage payment. The sender may employ a postage meter certified by the USPS (or the postal service of another country) to generate the indicium. The indicium is generally printed on a meter tape (which is later attached to the mailpiece) or directly onto the mailpiece itself, using a printer associated with the postage meter, which may be, for example, an inkjet printer, a thermal transfer printer, or a laser printer. The indicium can subsequently be authenticated by the USPS. For example, an optical scanning device may be used to read the indicium and a verification algorithm may be used to verify the authenticity of the indicium (e.g., by decoding and interpreting information contained within the indicium).
As is known, a number of different postal indicia are specified by and permitted by the USPS. One particular type of indicium is specified in the USPS's Information Based Indicia Program (IBIP). An IBIP indicium includes both a machine readable portion and a human readable portion that may contain (without limitation) information related to the paid postage amount, the issuance date, the postage meter identification number, a postal service symbol, and the class of service. The machine readable portion is typically comprised of a Data Matrix symbology (i.e., a two-dimensional barcode) which may carry cryptographically protected information, such as the postage amount and other postal data that relates to the mailpiece and to the postage meter that prints the indicium. The encrypted information, which is usually referred to as a digital token or a digital signature, is used for authentication purposes. The encryption is also used to protect the integrity of the information, including the postage amount, imprinted on the mailpiece for later verification of postage payment. Since the digital token incorporates encrypted information relating to evidencing of postage payment, altering the printed information in an indicium is detectable by standard authentication procedures. Examples of systems that are capable of generating and printing such indicia are described in U.S. Pat. Nos. 4,725,718, 4,757,537, 4,775,246 and 4,873,645, each assigned to the assignee of the present invention.
One security problem that exists with the use of IBIP indicia relates to copying of the indicia for reuse. More specifically, a thief may attempt to re-use an indicium by making copies of an indicium on different pieces of meter tape. The piece(s) of meter tape with the copied indicium is then applied to a mail piece and deposited in the mail, without the thief having paid for the postage. Compounding this problem is the fact that technology has become so advanced that even standard consumer devices, such as photocopiers and printers, are capable of producing credible copies of the indicium (i.e., detection of the copied postage is difficult).
Another security problem relates to a single indicium being printed multiple times. For example, a thief may tamper with the postage meter device such that an indicium is printed multiple times (e.g., on different portions of the meter tape, on different mailpieces, etc.) even though the postage amount paid was intended to be associated with a single use.
Thus, there exists a need for a mail metering system that can generate indicia with suitable security properties to allow detection of fraudulent use of the indicia.